The present invention relates to a piezoelectric/electrostrictive device comprising a movable portion being operated based on a displacement of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device capable of detecting a displacement of a movable portion by a piezoelectric/electrostrictive element, and more particularly relates to a piezoelectric/electrostrictive device which is superior in mechanical strength, impact resistance, and humidity resistance and is capable of having the movable portion efficiently operated in a large magnitude.
In recent years, in the fields of optics and magnetic recording, precision machining, and the like, a displacement element capable of adjusting an optical path length and position in sub-micron order has been required, and development has been progressed of the displacement element utilizing displacement due to the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric substance or the like). For example, as shown in FIG. 14, a piezoelectric actuator 21, in which a fixing portion 25, a movable portion 24, and a beam 26 connecting the two are integrally formed by providing a hole 28 on a plate-like body composed of a piezoelectric/electrostrictive material, and an electrode layer 22 is provided on the beam 26, is disclosed (in the official gazette of Japanese Patent Application Laid-Open No. 10-136665). In the actuator 21, when a voltage is applied to an electrode layer 22, the beam 26 expands or contracts in a direction in which the fixing portion 25 is connected with the movable portion 24 by the inverse piezoelectric effect or the electrostrictive effect, thus making it possible to have the movable portion 24 perform an arc-shaped displacement or a rotational displacement in the plane of the plate-like body.
On the other hand, JP-A-63-64640 discloses a technique with regard to an actuator utilizing a bimorph, in which an electrode of the bimorph is split, and by selecting the split electrodes to drive the actuator, precise positioning is performed at a high speed, and for example, the specification shows in FIG. 4 thereof a structure which uses two bimorphs opposed to each other.
However, in the above-described actuator 21, as the displacement in an expanding or contracting direction (namely, the in-plane direction of the plate-like body) of a piezoelectric/electrostrictive material is transmitted per se to a movable portion, there is a problem that an operational quantity of the movable portion 24 is small. Further, the actuator 21, having all the members thereof being composed of a piezoelectric/electrostrictive material which is fragile and comparatively heavy, has another problem, in addition to being low in mechanical strength, and inferior in handling, impact resistance and humidity resistance, that the actuator 21 per se is heavy and is operationally likely to be subjected to an influence of harmful vibrations (for example, residual vibrations or noise vibrations when operated at a high speed).
In order to solve the above-described problems in the actuator 21, a proposition has been made that an elastic filling material is filled into a hole 28. However, when the filling material is used, it is apparent that the efficiency of displacement due to the inverse piezoelectric effect or the electrostrictive effect is decreased.
On the other hand, what is shown in FIG. 4 of the laidopen specification of JP-A-63-64640 is the structure wherein so-called piezoelectric/electrostrictive portions, which generate displacement, bridge over both of the respective bonding portions in the bonding manner between the intermediary member and the bimorph, and the head and the bimorph; that is, the bimorph is formed continuously over from the intermediary member to the head. Therefore, there is observed an interference between the displace movement that occurs from the bonded portion between the intermediary member and the bimorph, and the displace movement that occurs from the bonded portion between the head and the bimorph as a fulcrum, thereby the expression of the displacement is prohibited. As a result, an action for effectively displacing the head per se toward the outer space is unable to be obtained. In addition, the actuator disclosed in JP-A-63-64640 is so structured that a displacement generating member and a so-called frame member (intermediary member or the like) are separately prepared, and then adhered to be incorporated, and consequently the bonded state of the frame with the bimorph is so structured to be likely to vary with time in accordance with operation of the bimorph, and also to be likely to cause drifting, exfoliation, or the like. Further, a bonded portion of the bimorph with the intermediary member and a bonded portion of the head with the bimorph, namely a structure having an adhesive agent at a supporting portion of a displacement member, is low in rigidity of the supporting portion, and is so structured that an increase in resonant frequency which is required in high speed operation is also difficult to be obtained.
Of a piezoelectric/electrostrictive device capable of solving such problems, although the applicant of the present invention and others have proposed, in the specification of the Japanese Patent Application No. 11-375581 filed on Dec. 28, 1999, a piezoelectric/electrostrictive device capable of obtaining a large displacement quantity as well as maintaining mechanical strength of a joined portion of a thin plate portion with the movable portion above a predetermined level, a device capable of generating still larger displacement and responding at a higher speed is sought after particularly for precise positioning in the magnetic recording field and optical field.
The present invention is made in view of above-described current situation, and an object thereof is to provide a displacement element which is capable of further increasing a displacement quantity of a movable portion while maintaining the mechanical strength at the joined portion of the thin plate portion with the movable portion above a predetermined level, as well as high in resonant frequency and superior in responsibility, and a sensor element capable of detecting vibrations of the movable portion in finer precision.
According to the present invention, firstly provided is a piezoelectric/electrostrictive device comprising a driving portion to be driven by displacement of a piezoelectric/electrostrictive element, a movable portion to be operated based on the drive of the driving portion, and a fixing portion for holding the driving portion and the fixing portion, the fixing portion and the movable portion being coupled together via the driving portion, and a hole being formed by inner walls of the driving portion, an inner wall of the movable portion, and an inner wall of the fixing portion, in which the driving portion is composed of a mutually opposed pair of thin plate portions and at least two piezoelectric/electrostrictive elements provided on the thin plate portions; each of said piezoelectric/electrostrictive elements being comprised of one or more pairs of electrodes and a piezoelectric/electrostrictive film; at least one of ends of said piezoelectric/electrostrictive element and a piezoelectric/electrostrictive operating portion on said at least one of ends are positioned on the fixing portion, and formed as being extended to at least a part of either one of the thin plate portions out of said pair of the thin plate portions, and an end of said piezoelectric/electrostrictive operating portion on another side of said piezoelectric/electrostrictive element is positioned on said either one of the thin plate portions, in a direction of said one of the thin plate portions from the fixing portion toward the movable portion, in one out of at least two piezoelectric/electrostrictive elements comprising at least one or more pairs of electrodes and a piezoelectric/electrostrictive film, at least one of the ends of said piezoelectric/electrostrictive element and a piezoelectric/electrostrictive operating portion on said at least one of the ends are positioned on the movable portion, and formed being extended to at least a part of another thin plate portion out of said pair of the thin plate portions, and an end of said piezoelectric/electrostrictive operating portion on another side of said piezoelectric/electrostrictive element is positioned on said another thin plate portion, in a direction of said another thin plate portion from the fixing portion toward the movable portion, in one of remaining piezoelectric/electrostrictive elements among said piezoelectric/electrostrictive elements comprising at least one or more pairs of electrodes and a piezoelectric/electrostrictive film.
According to the present invention, further provided is a piezoelectric/electrostrictive device in which the piezoelectric/electrostrictive element comprising one or more pairs of electrodes and a piezoelectric/electrostrictive film is further arranged on the outer surface of at least either one thin plate portion out of a pair of mutually opposing thin plate portions and has a structure, in a direction of the thin plate portion from a fixing portion toward a movable portion, at least one end of the piezoelectric/electrostrictive element and a piezoelectric/electrostrictive operating portion of the same end side thereof are arranged on the fixing portion or the movable portion, and formed being extended to at least a part of the thin plate portion, and an end of the piezoelectric/electrostrictive operating portion of the other end side of the piezoelectric/electrostrictive element is arranged on the thin plate portion, and the piezoelectric/electrostrictive element is arranged on the same thin plate portion opposing to one of the at least two piezoelectric/electrostrictive elements arranged so as to be in diagonal directions across a hole; and a piezoelectric/electrostrictive device in which, on respective outer surfaces of a pair of mutually opposing thin plate portions, in a direction of the thin plate portions from the fixing portion toward the movable portion, a piezoelectric/electrostrictive element comprising at least one or more pairs of electrodes and a piezoelectric/electrostrictive film, one end of the element and one end of a piezoelectric/electrostrictive operating portion positioned on said one end of the element being arranged on the fixing portion, and a piezoelectric/electrostrictive element comprising at least one or more pairs of electrodes and a piezoelectric/electrostrictive film, one end of the element and one end of a piezoelectric/electrostrictive operating portion positioned on said one end of the element being arranged on the movable portion, are respectively arranged mutually opposed on the same thin plate portion being extended until at least a part of said thin plate portion, the respective piezoelectric/electrostrictive elements having one end thereof and piezoelectric/electrostrictive operating portions on the same end side thereof are arranged on the fixing portion or the movable portion, and formed being extended to at least a part of the thin plate portion, and an end of a piezoelectric/electrostrictive operating portion of the other end side of the piezoelectric/electrostrictive element is arranged on the thin plate portion.
Furthermore, according to the present invention, provided are a piezoelectric/electrostrictive device in which ends of piezoelectric/electrostrictive operating portions on the thin plate portions of respective piezoelectric/electrostrictive elements provided mutually opposed on the outer surfaces of the same thin plate portions are arranged in positions not to exceed one half of the lengths of respective thin plate portions; a piezoelectric/electrostrictive device in which two piezoelectric/electrostrictive elements provided mutually opposed on the outer surface of the same thin plate portion share a piezoelectric/electrostrictive film; a piezoelectric/electrostrictive device in which two piezoelectric/electrostrictive elements provided mutually opposed on the outer surface of the same thin plate portion out of a pair of mutually opposing thin plate portions are elements mutually having the same or different functions; a piezoelectric/electrostrictive device in which two piezoelectric/electrostrictive elements provided mutually opposed on the outer surface of the same thin plate portion out of a pair of mutually opposing thin plate portions are elements having mutually different functions; a piezoelectric/electrostrictive device in which piezoelectric/electrostrictive elements existing mutually in diagonal directions across a hole out of at least two piezoelectric/electrostrictive elements provided on the outer surface of a pair of mutually opposing thin plate portions are elements having the same function, and a piezoelectric/electrostrictive device in which piezoelectric/electrostrictive elements existing in mutually diagonal directions across a hole out of at least two piezoelectric/electrostrictive elements provided on the outer surfaces of a pair of mutually opposing thin plate portions are elements having mutually different functions, and a piezoelectric/electrostrictive device in which at least one piezoelectric/electrostrictive element out of at least two piezoelectric/electrostrictive elements provided on the outer surfaces of a pair of mutually opposing thin plate portions has a multi-layered piezoelectric/electrostrictive operating portion.
In the present invention, it is observed that suppression of the rotation-mode displacement is a matter of great importance in a structure of a unique device disclosed in this specification, in view of enlarging displacement quantity of the movable portion and increasing efficiency of the displacement.
The rotation-mode herein means a displacement mode of a device as a whole; said displacement mode being obtainable by making a radius of curvature of one thin plate portion out of a pair of mutually opposing thin plate portions when said one thin plate portion over a whole length there is compulsively bent (hereinafter thus formed radius of curvature referred to as compulsive radius of curvature) smaller than that of another thin plate portion which is positioned on the opposite side of the center of curvature of the compulsive radius of curvature of said one thin plate portion when said another thin plate portion is bent according to the compulsive bent of said one thin plate portion. In other words, it is called a rotation-mode because a movable portion seems as if to largely rotate about a fixing portion.
In the rotation-mode, a distance of a point of the movable portion prior to and after the displacement is a function of the above-described compulsive radius of curvature and separation distance of a pair of mutually opposing thin plate portions. That is, the smaller the compulsive radius of curvature is (namely, the larger the bending of the thin plate portions is in the entire length), and the smaller the separation distance is, the larger the displacement distance becomes.
However, the separation distance cannot be made zero, as it is required in order to secure compulsive radius of curvature. In other words, there should be an allowance to allow one thin plate portion out of a pair of thin plate portions to be compulsively bent relative to the other thin plate of the pair of thin plates. The allowance can be made practically zero by using only one thin plate portion, however, such structure is undesirable in view of stability of the device, and in any case there is an upper limit.
As a movable portion displaces as if to largely rotate about a fixing portion as described previously, inner walls of the movable portion are made to form an angle relative to the fixing portion prior to and after the displacement.
As to such problem, the present invention provides a method to enable the movable portion to efficiently develop a large displacement by changing the displacement form of a thin plate portion to a displacement mode having a point of inflection existing on the thin plate portion, more specifically, having the point of inflection existing on the thin plate portion so as to have the curvature center for the bending existing on both sides of the thin plate portion interposed therebetween, at both portions of the thin plate portion having the point of inflection interposing therebetween, thus making a displacement mode for the device as the entirety, namely a rotational symmetric mode, which is a characteristic of the present invention.
This can be described that a method is found to deform a thin plate portion in an S-shape with a point of inflection existing on the thin plate portion, by bending a part of the thin plate portion containing a connecting portion of the thin plate portion with the fixing portion, or a connecting portion of the thin plate portion with the movable portion.
The rotational symmetric mode used herein means a displacement mode which can be most efficiently obtained when an S-shape of one thin plate portion out of a pair of mutually opposing thin plate portions is rotationally symmetric to the other thin plate portion using a hole formed by respective inner walls of the movable portion, driving portion, and fixing portion as the symmetric center of the rotational symmetry.
Although a distance of a point of the movable portion prior to and after the displacement at this time is a function of radius of curvature of the bent portion of the thin plate portion and a position of point of inflection on the same thin plate portion, the degree of freedom is high as there is no limitation factor being contrary to each other in a case of the rotational mode (whereas the entire length of the thin plate portion is desired to be bent, separation distance between a pair of thin plate portions which is a space for bending thereof is preferred to be smaller). This is better suited for efficiently developing a larger displacement, as bending even small parts of the thin plate portions can be utilized.
Further, contrary to the rotational mode, as an inner wall surface of a movable portion prior to displacement and the inner wall surface of the movable portion after the displacement maintain a paralleling state prior to and after the displacement, no unfavorable influence is given to the operation efficiency of other elements placed on the movable portion, thus a large displacement can be efficiently achieved.
In this way, as a concrete means for realizing the rotationally symmetric mode, at least two piezoelectric/electrostrictive elements and piezoelectric/electrostrictive operating portions thereof, of which respective ends are arranged on the movable portion or the fixing portion, and the other ends are arranged on the thin plate portions, are arranged so as to be in mutually diagonal directions at least with a hole interposing therebetween, for the above-described pair of mutually opposing thin plate portions. Thus, a displacement of the movable portion in the rotational mode is effectively suppressed, and as a result, a piezoelectric/electrostrictive device which develops an extremely large displacement in one axis direction is realized.
A piezoelectric/electrostrictive device of the present invention preferably comprises a movable portion, thin plate portions, and a fixing portion integrally formed in ceramics, and more preferably is made of materials containing fully-stabilized zirconia as the major component or materials containing partially stabilized zirconia as the major component, and most preferably at least the movable portion, the thin plate portions, and the fixing portion are made in a sintered ceramic green laminated body. This is because connecting portions with the movable portion, the thin plate portions, and the fixing portion can be made as a borderless structure by sintering integration, thus improving long term reliability of such portions over time, and in addition a phenomenon such as drifting or the like which is a variation with time of displacement as a device can be suppressed to the minimum, thus developing a large displacement with good reproducibility. Fabricating methods of the device according to the present application will be described later in detail.
By the way, when fabricating a device of a structure according to the present application, another method in addition to complete integration by sintering is that a laminated body divided in a mutually opposing direction of the thin plate portions, namely, a ceramic laminated body comprising a thin plate portion and a member to be a rectangular fixing portion and movable portion is prepared, a piezoelectric/electrostrictive element is formed by screen printing so as to overlap the thin plate portions and the fixing portion or the movable portion of the ceramic laminated body, at least two sintered structures integrated with the ceramic laminated body by sintering are prepared, and the sintered structures are adhered to so as to have the thin plate portions mutually away, that is, the above-described members that provide the fixing portion and the movable portion are mutually adhered to by use of an adhesive (for example, an organic adhesive such as epoxy resin, acrylic resin, or the like, and an inorganic adhesive such as glass, cement, or the like). However, since the device fabricated all in one by sintering is superior in stability and reliability even if a stress is applied to a device by operation of a driving portion, as it has no discontinuous portion of a so-called structured body such as a bonded portion where a third party intervenes, it is preferable to form the device by sintering integration where no adhesive or the like is used.
Further, in a piezoelectric/electrostrictive device according to the present invention, it is preferable that a piezoelectric/electrostrictive film comprising a piezoelectric/electrostrictive element is made of the material whose major component is a mixture of lead zirconate, lead titanate, and lead magnesium niobate, and also preferable is one made of materials containing sodium bismuth titanate. Details of materials to be used will be described later.
It should be noted that xe2x80x9ca piezoelectric/electrostrictive device (hereinafter referred to only as a xe2x80x9cdevicexe2x80x9d)xe2x80x9d in the present specification is a notion to imply an element mutually converting an electric energy and a mechanical energy by way of a piezoelectric/electrostrictive material. Therefore, the device is preferably used as an active element such as a variety of actuators, vibrators, or the like, and more specifically as a displacement element utilizing a displacement due to the inverse piezoelectric effect or the electrostrictive effect. However, it can also be used as a passive element such as an acceleration sensor element, an impact sensor element, or the like. It should also be noted that xe2x80x9cpiezoelectricxe2x80x9d in the present specification means xe2x80x9cpiezoelectric/electrostrictivexe2x80x9d. Further, a xe2x80x9clengthxe2x80x9d means a distance in a direction connecting a movable portion with a fixing portion, namely in the Z-axis direction in the drawings, a xe2x80x9cwidthxe2x80x9d means a distance in a direction penetrating through a hole, namely in the Y-axis direction in the drawings, and a xe2x80x9cthicknessxe2x80x9d means a distance in a laminating direction of a piezoelectric/electrostrictive element with a thin plate portion, namely in the X-axis direction in the drawings.
A piezoelectric/electrostrictive element means an element comprising at least one or more pairs of electrodes and a piezoelectric/electrostrictive film to be driven based on signals transmitted, and to perform a function of conveying the movement thereof to a movable portion. In the element, a piezoelectric operating portion means, the substantial operable portion of a piezoelectric/electrostrictive element so as to move a movable portion in a predetermined movement in accordance with an applied signal to a driving portion, and comprises a portion where at least one or more pairs of electrodes and a piezoelectric/electrostrictive film are mutually overlapped. Further, a base for a device means a sintered ceramic laminated body prior to arrangement of a piezoelectric/electrostrictive element thereon. In addition, in the present invention, displacement quantity of a device is measured by a laser Doppler vibrometer (made by Graphtec Corp.).